The invention relates to a drier for a lacquering line for drying freshly lacquered articles.
In a specific, commercially known drier of having several drying, sections a separate heating unit is associated with each drier section. Each such heating unit generates its own heated primary gas flow, which is directed into the interior of the drier housing and conveyed there through a heat exchanger, which in turn is in thermal contact with the circulated air. Said style of construction is extremely expensive because it requires a plurality of heating units and heat exchangers.
Another drier is described in EP-A-0 706 021. Here, the hot primary gas flow generated by a central heating unit is conveyed through a double-walled line situated in the interior of the drier housing. Depending on the position of control flaps provided in sections, the hot primary gas is conveyed through the respective drier section inside the inner pipe and is therefore not available as a heat source for the circulated air or through the gap between the inner pipe and the outer pipe, which serves as a heat-exchanging surface for the air circulated in the relevant section. Said style of construction is also expensive, difficult to clean and maintain and takes up too much space on account of the hot primary gas line extending inside the drier housing. In the event of leakage from the primary gas pipe, primary gas may pass into the circulating air of the drier, which may cause lacquering defects. Furthermore, heat radiation and convection may not be adjusted independently of one another.
The object of the present invention is to refine a drier of the type defined initially in such a way that it is inexpensive to manufacture and easy to maintain.
The object is achieved by the drier of the invention. The drier comprises:
a) a drier housing;
b) a plurality of drier sections inside the drier housing, in each of which air may be circulated with the aid of at least one fan;
c) at least one heating unit, which generates a hot primary gas flow;
d) at least one heat exchanger, via which the air circulating in the drier sections is heated by the primary gas;
whereby
e) the temperature of the air circulating in the various drier sections is individually adjustable.
f) for the plurality of drier sections a common heating unit and, downstream of the latter, a common fresh-air heat exchanger are provided;
g) the hot fresh air flow generated by the fresh-air heat exchanger is introducible through a distribution line and an appropriate number of branch lines into the various drier sections,
wherein
h) in each branch line an adjustable control flap is disposed.
The fact that only one heating unit and only one heat exchanger need be provided in a drier according to the invention already means that costs are considerably reduced. This is true even though the common heating unit and the common fresh-air heat exchanger have to be of a larger capacity than each of the heating units and heat exchangers used in prior art. Because of the heating of the circulated air by the heated fresh air supplied in metered quantities via the control flaps, very much fewer structural components are needed and take up space inside the drier housing. Owing to the reduced costs it is possible to provide the drier according to the invention with a higher number of drier sections, thereby enabling finer adjustment. of the object temperature curve. Whereas in prior art the circulation fans had to overcome the pressure drop at the heating units and heat exchangers, this is no longer necessary with the refinement of the drier according to the invention. The circulation fans may be of a smaller design and require less energy. Also, in heat-up mode less energy is consumed because there are fewer masses to heat up than in prior art.
In an advantageous embodiment of the invention, the heating unit is a regenerative thermal afterburning apparatus, to which the solvent-containing outgoing air from the drier housing is supplied. Thus, in a manner known as such, the solvent which has transferred to the circulating air is disposed of and at the same time at least some of the energy demand required for drying is covered.
Alternatively, however, the heating unit may be a gas burner or a steam generator.